Can-bus J1939 onto N2k for HVAC?

[wkearney99]

Apparently Dometic AC controls can have a Can-bus board added to them. Each board can be configured with it's own Canbus device and group ID. Which I think means they can share a Can-bus.

That and Maretron's J2K100 can be used to bridge that onto an NMEA-2000 bus. Does anyone know if the J2K100 can bridge for more than one device on the Can-bus? Or is it just one?

And are there any other devices that'll bridge more than one Can-bus device onto an N2K network?

[Tehani]

wkearney99,
The question is not so easy. A CAN bus can work at any speed up to 1Mbps. Not all systems based on that bus operate at 250 Kbps. There are also devices in many areas of the industry that work with 11-bit IDs instead of the 29 bits of NMEA2000.
I do not know these two details in the case of Dometic, but I can assure you that, although they are the same as in N2k (already difficult), you will not be able to share the bus because the network management will be different.
The J1939 system uses a network protocol identical to NMEA2000, and in spite of everything, note that the Maretron J2K100 has 2 CAN connectors. That has 2 possible reasons, one is the galvanic isolation, and another to avoid that possible PGN's own J1939 that do not interest anyone, are present in NMEA2000. (Filtering function). It also performs a J1939 compilation of the normalized data in NMEA2000 and generates the corresponding PGNs.
One more thing: J1938 is designed to use a group of instruments for each engine. When two motors with J1939 output are installed, it is necessary to assign an instance to each motor when transferring the data to the common NMEA2000 network. This is done by configuring the J2K100. That is why it is necessary to install two Maretron when there are two motors.

[wkearney99]

Fair points. I've got two of the Yacht Design interfaces connected to my Caterpillar C-12 engines.

I wasn't expecting to splice or otherwise 'join' the N2K and J-1939 networks directly. That would certainly be problematic.

I'm just wondering that for what's likely to be a low data rate setup like HVAC controllers if there isn't a way to have just one bridge from them to the N2K bus. Otherwise it's four bridges.

[Tehani]

It is very possible that you have two devices that generate data in each engine. Not the entire block is motor, also esite the gear unit and / or the jets. These data are sent separately.

[Tehani]

Mmmmm, I think you should have started this thread in the Electronics comms / AV section.

[wkearney99]

Originally Posted by Tehani

It is very possible that you have two devices that generate data in each engine. Not the entire block is motor, also esite the gear unit and / or the jets. These data are sent separately.

No, I'm not talking about the engines here, that's handled, I get a reasonably complete range of engine data for those. I don't have the transmissions connected, at least not yet.

[wkearney99]

Originally Posted by Tehani

Mmmmm, I think you should have started this thread in the Electronics comms / AV section.

True, but much like fishing, some sub-forums are better than others for getting results. I figured this is more of an instrumentation question than a specific electronics question. Thus OpenCPN being a bit of a catch-all for various networked devices.. it seemed reasonable to ask here.

[wkearney99]

To follow up, the Micro Air folks make some thermostats that look like they'll suit my application. Having my HVAC contractor look into it in more detail. Upside is their Can-bus implementation would support being bridged by just one NMEA interface, not one PER unit.

[leftbrainstuff]

Why connect HVAC to your NMEA2000 system? Assuming your NMEA2000 system is for mission and safety critical nav and related systems?

[wkearney99]

There's plenty of 'head room' on the N2K bus to handle the data. If not it's pretty trivial to separate them.

[anthem00]

Just to answer your original question. Th j2k100 adapts one j1939 device to nmea2k. It isolates that on the nmea2k network using instance ids. Now whether you can bond more devices on can before bridging that’s an entirely different discussion.